The Northern Alberta Tar Sands are considered to be one of the world's largest remaining repositories of oil. The tar sands are typically composed of about 70 to about 90 percent by weight mineral solids, including sand, silt and clay, about 1 to about 10 percent by weight water, and a bitumen or oil film, that comprises from trace amounts up to as much as 21 percent by weight.
Unlike conventional oil reserves, the bitumen is extremely viscous and difficult to separate from the water and mineral mixture in which it is found. Generally speaking, the process of separating bitumen from the tar sands comprises five broad stages. Initially in the first stage, the oil sand is excavated from its location and passed through a crusher, or “sizer,” to break down or comminute the ore into conveyable pieces. The crushed ore is then typically combined with hot process water to aid in liberating the oil. The combined comminuted tar sand and hot water is typically referred to as a “slurry.” Other agents, such as chemical aids (for example including caustic, surfactant, pH adjuster, dispersant) may be added to the slurry.
The slurry is passed through a slurry box in which the slurry is allowed to mix and dwell for a period, primarily to ensure a proper suction head and a constant flow of slurry to a slurry pump. The slurry output from the slurry box is pumped through a hydrotransport conduit and preferably transported an appropriate distance to condition the slurry, and is typically passed through an extraction facility for separating the bitumen froth from the slurry. Typically the mineral matter is separated from the slurry using specific gravity separation, such as PSV's (Primary Separation Vessels) and hydrocyclones. After the slurry has been processed to remove the optimal amount of bitumen, the remaining material (commonly referred to as tailings) is typically routed into a tailings deposition site.
It has been recognized that, since the bitumen comprises a relatively small percentage by weight of the ore initially extracted, separation of the mineral content from the ore as soon as possible after excavation would lead to the most efficient and cost effective mining process.
Over the years, a variety of processes have been used to process and transport the ore from the excavation site. Initially, oil sand excavation and transport were completely mechanical via trucks or conveyor belts from the mine face to a large facility for crushing and conditioning the tar sand. As described in Canadian Patent No. 2,029,795, it was determined that it was preferable to crush the ore at a slurry preparation facility located at an intermediate site and combine the ore with hot process water to create a slurry in which could be hydraulically transported by a pipe. This “hydro-transport” process served the dual purpose of efficiently transporting the slurry from a site near the mine face to a more permanent facility and allowing time for the slurry to be sufficiently conditioned on route. Provided the hydro-transport was over a large enough distance that the dwell time in the pipe was sufficiently long, the slurry would arrive at the separation facility already conditioned. Thus, the previously required separate conditioning step could be omitted from the process.
While hydro-transport solved some of the difficulties with transporting the ore from the mine site face to the separation facility, it did not address the fact that in open pit mining the mine site face moves as ore is excavated, increasing the distance to the slurry facility. Solutions to date have typically relied on constructing longer conveyor belts to transport the ore, or use additional trucks, to move the ore from the mine face to the slurry facility at the intermediate site.
Prior art slurry facilities are stationed in a fixed location. There thus exists a need to increase the efficiency of excavation and transport processes to reduce operating costs.
It would accordingly be advantageous to provide an apparatus for creating a slurry that is mobile and can be advanced as the distance from the slurry facility to the mine face increases.